this change to the environment makes an undesirable behavior difficult

…one of the most successful public health campaigns of the last half-century is the effort in the United States to reduce the number of smokers. One of the most important factors that decreased smoking rates among adults from roughly 50% in the 1960s to about 20% now is the environment. It is no longer possible to smoke in public buildings in most places in the United States. Some businesses no longer allow smoking on their entire campuses. This change to the environment makes an undesirable behavior difficult.